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JEE PYQ: Binomial Theorem Question 29

Question 29 - 2020 (07 Jan Shift 1)

The greatest positive integer $k$, for which $49^k + 1$ is a factor of the sum $49^{125} + 49^{124} + \ldots + 49^2 + 49 + 1$, is:

(1) 32 (2) 63 (3) 60 (4) 65

Show Answer

Answer: (2)

Solution

Sum $= \frac{49^{126}-1}{48}$. $49^k + 1$ divides $49^{63}+1$ when $k | 63$. Largest $k = 63$.


Learning Progress: Step 29 of 55 in this series